1. Technical Field
The present invention relates to a power unit and a safety circuit having the same, and more particularly to a structure for preventing an electric shock, which would otherwise arise during maintenance operation
2. Related Art
In a hybrid electric vehicle, or the like, using a power unit assembled by a series connection of a plurality of battery modules, each of which consists of one cell or a plurality of cells, provision of only a power switch for opening or closing a current-carrying circuit originating from a power unit is assumed not to prevent erroneous activation of a power switch during maintenance operation. For this reason, provision of an interlock mechanism separate from the power switch has been proposed.
2001-320801 A describes a configuration having a safety switch interposed between an arbitrary pair of battery modules in which an operator inserts and removes a service plug into and from the breaker main unit, thereby opening or closing a connection among battery modules and consequently opening and closing the current-carrying circuit. There is also described a configuration in which an interlock lead switch is turned off as a result of removal of the service plug, thereby deactivating a system main relay in a master control section.
2006-294425 A describes a configuration having a safety switch interposed between an arbitrary pair of battery modules in which an operator inserts and removes a safety plug into and from the breaker main unit, thereby opening or closing a connection among the battery modules, as well as describing provision of a key for hindering insertion of the safety plug in a state of being attachable and attached to the breaker main unit.
FIGS. 6, 7A, and 7B show the configuration of a related-art battery pack. A battery pack 1 is for driving a vehicle. A plurality of battery modules made up of one cell or a plurality of series-connected cells are arranged in parallel with cooling passages interposed therebetween. The battery pack includes a built-in battery assembly constructed by binding and assembling end members disposed at both ends of the battery modules and connecting the battery modules in series with each other. A cooling air ventilation passage for supplying and exhausting a cooling air to and from the respective cooling passages provided between the battery modules is laid in upper and lower portions of the battery assembly. A charge/discharge monitoring section (a battery ECU) where equipment for monitoring a voltage, a current, a temperature, an SOC (State of Charge), and the like, of a battery pack is provided on one side surface of the battery assembly, and a fan for supplying a cooling air to the cooling air ventilation passage is provided on the other end of the battery assembly.
A safety switch 2 for opening and closing a current-carrying circuit among arbitrary interconnected battery modules is provided in a middle position on one side surface of the battery pack 1. The safety switch 2 is made up of a switch main body 3 and a safety plug 4 and configured in such a way that the current-carrying circuit is closed by insertion of the safety plug 4 and that the current-carrying circuit is opened by removal of the safety plug 4.
FIGS. 7A and 7B show an electrical connection configuration of the battery pack 1. Mutually-adjoining battery modules 5 are wholly connected in series as a result of positive terminals and negative terminals of the battery modules 5 are sequentially connected to each other. All of the positive and negative terminals connected to both ends of the respective battery modules are connected to external connection terminals 7 by way of a main relay switch 6. Further, the positive and negative terminals of a pair of arbitrary, adjacent, intermediate battery modules 5 are connected to each other by way of the safety switch 2. A pair of connection terminals 3a are connected in parallel within the switch main body 3 of the safety switch 2, and the positive and negative terminals of the pair of battery modules 5 are connected to the connection terminals 3a. A pair of connection terminals 4a are provided opposite the connection terminals 3a on an insertion-side end face of the safety plug 4 of the safety switch 2 as shown in FIG. 7B. A pair of connection terminals 4a are connected to each other by way of a fuse 8, and the connection terminals 3a are connected together by way of the fuse 8 by insertion of the safety plug 4 into the switch main body 3. The current-carrying circuit is shut off by removal of the safety plug 4. The safety plug 4 is provided with a lock member 9 that is appropriately operated in a state of being inserted into the switch main body 3, to thus engage an engagement section 9a in a counterpart engagement section 10 formed in the switch main body 3, thereby locking an inserted state. Further, the safety plug 4 is provided with a detection switch 11 that operates when the lock member 9 is brought into a locked state. When the detection switch 11 operates, the control section 12 is configured so as to close the main relay switch 6.
As mentioned above, safety can be ensured during maintenance operation by adoption of the interlock configuration that opens and closes a connection between the battery modules by insertion and removal of a service plug (or a safety plug). However, a problem may arise when a terminal cover is removed during operation for performing maintenance and check on the neighborhood of the positive and negative external connection terminals of the battery modules. Specifically, it may also be the case where maintenance and check performance will be performed after removal of the service plug and the terminal cover and where a serviceman will insert the service plug by forgetting to attach the terminal cover after completion of the maintenance and check operation. In this case, the connection between the battery modules will be closed while the external connection terminals are left exposed.
As a matter of course, there is also a conceivable case where the geometry of a position where the service plug and the terminal cover are engaged with each other is provided with a specific pattern in order to enable insertion of the service plug only in a state of the terminal cover being attached. However, it has been expected to prevent the serviceman from forgetting to attach the terminal cover more simply, reliably.
When the power unit is equipped with a plurality of interlock mechanisms or when each of a plurality of power units is equipped with an interlock mechanism, operation of the power units must be controlled without fail in accordance with operating conditions of the interlock mechanisms.